Spending the summer in his grandfather's rundown town, ten-year-old Ben meets an adventurous local girl and together they learn that the town's veterinarian runs a secret hospital for imaginary creatures.
When they uncover a conspiracy against America and its fundamental freedoms, the Kidd children, accompanied by their great uncle, crisscross the country in a race to prove that a newly-discovered copy of the Bill of Rights is a forgery.